(1) Field of the Invention
The present invention relates to a real-time recording technique applicable to logical formats of read-only media.
(2) Description of the Related Art
A real-time recording technique is for encoding and recording video and audio signals that are sequentially input to a device, onto a recording medium in real time. One problem involved in real-time recording is “data requiring future prediction”. Data requiring future prediction used herein refers to data items, among those defined according to the logical format of the recording medium, having dependency on data to be generated after the current encoding time.
Normally, a logical format for read-only media is defined on a precondition that the volume image per optical disc is fixed before producing an original master for mass production. This concept of recording data after fixing the volume image per optical disc contradicts the concept of real-time recording signals input to a device, by sequentially encoding the signals in real time.
Consequently, when a recording device encodes and records data in real time according to a logical format defined for read only media, many of the data items turn out to be “data items requiring future prediction”. One exemplary logical format for read only media is called “DVD-Video”. When encoding and recording data by a recording device in real time according to this DVD-Video format, various data items contained in NV packs (navigation packs) require future prediction.
The “NV pack” mentioned herein is a pack of management data generated one for a predetermined number of GOPs (Groups of Pictures). Each time the encoder has generated the predetermined number of GOPs, the recording device generates an NV pack and multiplexes the NV pack, the GOPs, and audio data. The multiplexed data is called a VOBU (Video Object Unit). By generating a sequence of VOBUs, video and audio data digitized according to the DVD-Video format are recorded in units called VOBs (Video Objects). Among data items contained in each NV pack, the data items called FWDI 20, FWDI 60, FWDI 120, FWDI 240, and VOB_V_E_PTM are “data requiring future prediction”. The FWDI 20, FWDI 60, FWDI 120, and FWDI 240 in a specific NV pack indicate the numbers of packs present between the specific NV pack and the NV packs that belong to respective VOBUs containing picture data to be displayed 10 sec, 30 sec, 60 sec, and 120 sec after the video playback start time of the VOBU to which the specific NV pack belongs. That is to say, the content of each FWDI cannot be determined until encoding of the relative VOBU that is tens or even hundreds after the current VOBU are encoded.
However, in the case of recording media of a write-once type, such as DVD-R and DVD±R discs (hereinafter, collectively referred to as DVD±R), once VOBUs are recorded onto the DVD±R, it is no longer possible to modify the contents of FWDIs.
For this reason, it is required to hold VOBUs on a memory until the sizes of VOBUs tens and hundreds after a current VOBU are fixed. It is only after the sizes of those VOBUs are determined that the FWDI 20, FWDI 60, FWDI 120, and FWDI 240 can be set and the current VOBU are recorded onto the DVD±R.
In order to wait for VOBUs hundreds after a current VOBU to be generated, the above processing requires the memory to have a large capacity enough to temporally hold hundreds of VOBUs. As described above, when recording onto a write-once type recording medium, numerous VOBUs need be held on the memory before data items of each NV packs are determined. Consequently, a large-sized memory needs to be installed, which makes it difficult to reduce the cost of recording device.